The present invention relates to a magnetic recording/reproducing device equipped with an anisotropic magnetoresistive read head or a giant magnetoresistive read head, and more particularly to a device for suppressing errors due to fluctuations in read waveform during reproduction.
A magnetic recording/reproducing device generally comprises a medium for magnetically recording information, a write element for recording information on the medium, a read element for transducing changes in a magnetic field leaking from the medium into electrical signals, means for detecting output signals of the read element, means for controlling recording/reproducing operations, and positioning means for positioning the write and read elements relative to the medium. Known media include disk-like ones and tape-like ones, and disk-like media are classified into a type previously incorporated in a device and a replaceable type.
The write element and the read element are often integrally formed into a laminate so as to be used as a read/write composite head. In a magnetic disk device, which is a form of magnetic recording/reproducing device, a single or a plurality of read/write heads are moved above a desired track or tracks on a single or a plurality of disks to record information on the disk(s) or to reproduce information from the disk(s). As a positioning mechanism for the read/write heads, a rotary actuator using a voice coil motor is widely employed. The rotary actuator is a mechanism which has a rotating shaft outside the disks and rotates read/write heads mounted at the tip thereof above the disks to move the heads to desired positions.
For a write element, in turn, an inductive element having a coil for generating flux and a pair of magnetic cores for collecting the flux is mainly employed. The inductive write element performs a recording operation by passing a pulse-like recording current through the coil to apply a medium with a magnetic field generated by the write element. Employed for a read element is a magnetoresistive (MR) element which has a magnetoresistive layer and a pair of leads electrically bonded to the MR layer. The MR element may be generally classified into an anisotropic magnetoresistive (AMR) element applying the conventionally known AMR effect and a giant magnetoresistive (GMR) element applying a GMR effect. One type of GMR element is a spin valve head which is disclosed, for example, in JP-A-4-358310, which corresponds to U.S. Pat. No. 5,206,590. While no head employing a GMR element has been manufactured at present, studies on the GMR element have been advanced as an element of the next and subsequent generations because of its higher sensitivity than a head employing an AMR element.
As is well known in the art, the AMR element has an anisotropic magnetoresistive (AMR) layer which changes its electrical resistance by the action of a magnetic field, wherein a change in voltage is derived as an output signal when a constant current is applied to the AMR layer, while a change in current is derived as an output signal when a constant voltage is applied to the same. Although the AMR layer changes its electrical resistance, a resistance of the MR film is not in a proportional relationship with the applied field. Thus, for improving the linearity of the relationship between the applied magnetic field and an output signal of the AMR element, the AMR element often has a structure including a soft adjacent layer (SAL) or an electrically conductive bias layer laminated near the AMR layer. The SAL is magnetized by receiving a magnetic field generated by a bias current flowing through the AMR layer, and has a function of applying the AMR layer with a magnetic field generated by the magnetization as a bias field. The electrically conductive bias layer generates a magnetic field when applied with a bias current flowing therethrough, and has a function of applying the AMR layer with this magnetic field as a bias field. In either of the structures, a bias current is passed through the AMR element to apply the AMR layer with a bias field such that the AMR element can utilize a highly linear portion of the AMR layer characteristic.
The GMR element, on the other hand, has laminated GMR layers composed of a first ferromagnetic layer which changes a magnetization direction due to a magnetic field leaking from a medium, a second ferromagnetic layer having a fixed magnetization direction, and a non-magnetic conductor layer inserted between the first ferromagnetic layer and the second ferromagnetic layer. The GMR element changes its electrical resistance in response to a change in the angle between the magnetization direction of the first ferromagnetic layer and the magnetization direction of the second ferromagnetic layer. The second ferromagnetic layer is often laminated on/under an antiferromagnetic layer or a permanent magnet layer for fixing the magnetization thereof. The GMR element typically exhibits the best linearity when the magnetization direction of the first ferromagnetic layer is orthogonal to the magnetization direction of the second ferromagnetic layer. As is the case of the AMR element, a reproduced signal from the GMR element is detected by applying a constant current or a constant voltage current to the element, In this event, a portion of the detecting current flows through the non-magnetic conductor layer, the second ferromagnetic layer, and the antiferromagnetic layer or the permanent magnet layer for fixing the magnetization direction of the second ferromagnetic layer to generate a magnetic field which is applied to the first ferromagnetic layer as a bias field. Thus, the bias field causes the first ferromagnetic layer to change the magnetization direction. As described above, while the AMR element and the GMR element operate according to different principles, they have a common basis in that a bias current (which in many cases serves as a detecting current) flowing through the MR layer during a reproducing operation generates a bias field which is applied to the MR layer to rotate the magnetization of the MR layer.
In addition, the respective magnetic layers of the respective MR elements, particularly, the AMR layer and the SAL constituting the AMR element and the first ferromagnetic layer constituting the GMR element are desirably held in a single domain state in order to suppress magnetic noise and ensure the linearity between an applied magnetic field and an output signal. As known techniques for realizing this state, there is an approach which employs a domain control layer comprising a permanent magnet or laminated layers composed of a soft magnetic layer and an antiferromagnetic layer arranged at both end portions of each MR element in a track direction such that a magnetic field generated by the domain control layer is utilized to induce the single domain state. Also known is an approach in which an antiferromagnetic layer is directly laminated on both end regions of an AMR layer of an AMR element or of a first ferromagnetic layer of a GMR element to hold these regions in a single domain to induce a detecting portion positioned in a central region of the AMR layer or the first ferromagnetic layer (a region sandwiched by a pair of leads for transducing a change in magnetic field into an electrical signal) into a single domain state.